The present invention relates to microelectronic packages, to components for use in fabrication of microelectronic packages, and to methods of making the packages and components.
Microelectronic devices generally comprise a thin slab of a semiconductor material, such as silicon or gallium arsenide, commonly called a die or a semiconductor chip. Semiconductor chips are commonly provided as individual, prepackaged units. In some unit designs, the semiconductor chip is mounted to a substrate or chip carrier, which is in turn mounted on a circuit panel, such as a printed circuit board.
In one face of the semiconductor chip is fabricated the active circuitry. To facilitate electrical connection to the active circuitry, the chip is provided with bond pads on the same face. The bond pads are typically placed in a regular array either around the edges of the die or, for many memory devices, in the die center. The bond pads are generally made of a conductive metal, such as gold or aluminum, around 0.5 μm thick. The size of the bond pads will vary with the device type but will typically measure tens to hundreds of microns on a side.
Flip-chip interconnection is a commonly used scheme for conductively connecting bond pads on the semiconductor chip to contact pads on a substrate. In flip-chip interconnection, lumps of metal are typically placed on each bond pad. The die is then inverted so the metal lumps provide both the electrical pathway between the bond pads and the substrate as well as the mechanical attachment of the die to the substrate.
There are many variations of the flip-chip process, but one common configuration is to use solder for the lumps of metal and fusion of the solder as the method of fastening it to the bond pads and the substrate. When it melts, the solder flows to form truncated spheres.
Microcontact elements in the form of elongated posts or pins may be used to connect microelectronic packages to circuit boards and for other connections in microelectronic packaging. In some instances, microcontacts have been formed by etching a metallic structure including one or more metallic layers to form the microcontacts. The etching process limits the size of the microcontacts. Conventional etching processes typically cannot form microcontacts with a large ratio of height to maximum width, referred to herein as “aspect ratio”. It has been difficult or impossible to form arrays of microcontacts with appreciable height and very small pitch or spacing between adjacent microcontacts. Moreover, the configurations of the microcontacts formed by conventional etching processes are limited.
Despite the advances that have been made in flip chip interconnections, there is still a need for improvements in order to minimize the package thickness, while enhancing joint reliability. These attributes of the present invention are achieved by the construction of the microelectronic packages as described hereinafter.